Philipp Lenard

Philipp Lenard
(1862-1947)

German physicist, winner of the Nobel Prize for Physics in 1905 for
his research on cathode rays and the discovery of many of their properties.
His results had important implications for the development of electronics
and nuclear physics.
After serving as a lecturer and as an assistant to Heinrich Hertz at
the University of Bonn in 1893, Lenard was professor of physics successively
at the universities of Breslau (1894), Aachen (1895), Heidelberg (1896),
and Kiel (1898). In 1907 he returned to the University of Heidelberg
as professor of physics, where he stayed until his retirement in 1931.

Applying the discovery that cathode rays pass through thin leaves of
metal, Lenard constructed (1898) a cathode-ray tube with an aluminum
window through which the rays could pass into the open air. Using a
phosphorescent screen, he showed that the rays decreased in number as
the screen was drawn away from the tube and that they ceased at a distance.
The experiments also demonstrated that the power of substances to absorb
the rays depends on their density and not on their chemical nature and
that absorption decreases with increasing velocity of the rays. In similar
experiments in 1899 he proved that cathode rays are created when light
strikes metal surfaces; this phenomenon later became known as the photoelectric
effect.

Lenard's extensive research also included studies of ultraviolet light,
the electrical conductivity of flames, and phosphorescence. He wrote
a considerable number of books on cathode rays, relativity, and related
subjects, including Uber Kathodenstrahlen (1906; "On Cathode Rays")
and Deutsche Physik, 4 vol. (1936-37; "German Physics").